Leicester had initially hoped to have Tuilagi back in action in time for the December double header with Montpellier but the 22-year-old centre has now had surgery on his pectoral muscle after a period of rehabilitation failed to result in a full recovery.
Tuilagi suffered the injury in a domestic clash with Newcastle Falcons at Welford Road on September 21 and was provisionally expected to be out of action for approximately two months.
He missed the opening two rounds of Heineken Cup competition against Ulster and Benetton Treviso, with the 2001 and 2002 champions losing 22-16 in Belfast in his absence but beating the Italians with a bonus point on home soil.
As well as next month's encounters with Montpellier, the British & Irish Lions tourist will also sit out the trip to Treviso and what could be a crucial home tie with Ulster in January as Leicester look to build on last season's quarter-final exit at the hands of eventual tournament winners Toulon.
Tuilagi's absence is exasperated by a series of other injuries in the Leicester midfield, with Anthony Allen, Niki Goneva, Terence Hepetema, Matt Smith and Dan Bowden all having been sidelined.
Smith and Bowden are expected to recover from minor head knocks in time for this week's LV= Cup clash at Worcester but Allen and Hepetema won't face Montpellier, while Goneva remains a major doubt for the resumption of European competition.
Allen is out until at least the New Year with an unusual leg injury that is more commonly associated with road traffic accidents; Goneva is struggling with a calf injury; and New Zealander Hepetema, who was signed as injury cover for Smith earlier this term, suffered a fractured eye socket in the league defeat to Harlequins the week before last.
George Catchpole and Javiah Pohe were the centre pairing in Leicester's win over the Ospreys last Friday night but both are just 19 years of age and were making their first senior appearances.